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Pressure signs/chronographing

 
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  #1  
Old 01-08-2007, 02:01 PM
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Pressure signs/chronographing

Just got my first chronograph, graduating into a little more in depth reloading I guess, or a least gradually able to afford a few more tools!
My question is, while working up loads, are there indicators in velocity progression that indicate dangerous pressures?
I mean if your working up say .5 gr increments in your charges, what do you watch in your velocities and extreme spread to dictate what the pressure is doing?
I know a few of the simple indicators, primers flowing around the firing pin, split necks, difficult bolt opening, ejector pin marks on the case head, (are their any others?).
But from what I read on here it sounds loike ya'll can observe pressure with what the velocity does on your load work ups?? Just curious!
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Old 01-08-2007, 03:38 PM
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Re: Pressure signs/chronographing

[ QUOTE ]
... I know a few of the simple indicators, primers flowing around the firing pin, split necks, difficult bolt opening, ejector pin marks on the case head, (are their any others?).

[/ QUOTE ]

Split necks are not a sign of pressure, but the rest... "primers flowing around the firing pin, difficult bolt opening, ejector pin marks on the case head,"... are all you need to look for.

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Old 01-09-2007, 07:59 AM
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Re: Pressure signs/chronographing

Measure case head expansion.

Watch for huge MV jumps. if you do a ladder test you will find that your accuracy nodes coincide with MV nodes. ie normally the same say 3-4 bullets in a ladder that group together will also have very close MV while the one after will jump out of the group and in MV.

BH
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Old 05-05-2008, 03:12 PM
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Quote:
Originally Posted by Big_Tex22 View Post
Just got my first chronograph, graduating into a little more in depth reloading I guess, or a least gradually able to afford a few more tools!
My question is, while working up loads, are there indicators in velocity progression that indicate dangerous pressures?
I mean if your working up say .5 gr increments in your charges, what do you watch in your velocities and extreme spread to dictate what the pressure is doing?
I know a few of the simple indicators, primers flowing around the firing pin, split necks, difficult bolt opening, ejector pin marks on the case head, (are their any others?).
But from what I read on here it sounds loike ya'll can observe pressure with what the velocity does on your load work ups?? Just curious!
The simple answer is that velocity is the single greatest indicator of pressure that we have without using pressure testing equipment.

Here's the best way I know to describe it. The manufactures work up their data to SAAMI pressure specs, and in fact, usually stay about 2-3K psi under SAAMI max. I'll tell you how I work up my loads. I'll use the 30-06 as an example. I look up data from several sources. I like Nosler data, and Alliant powder seems to be good for me too. Alliant says 60 grs R-22 and a 165 Nosler Partiton get 2755 in a 24" bbl at 51K psi. Nosler says that same powder charge gets 2850. It doesn't give a pressure, but they're loading right up to 60K psi, and they say max is 63grs at 3002fps. (Some would say this is hot) So, at the same powder charge with the same bullet, you got a 100fps difference. Well, looking at most data you'll find that most max velocity given for most 165 bullets will top out around 2850-2950. So, with R-22, you start working up from say 57 grains, and when you hit that velocity range (assuming a like legth bbl), you've found your max load. Slower powders give better velocity with less pressure. If you went with H4350, then you might top out on the low end of that velocity range. In my experience, you can't get enough R-22 in the 30-06 with 165s to do any damage or even get pressure signs. In my 30-06 with a 23.6" bbl 60grs of R-22 and a 165 Hornady gets 2875. I shoot as my hunting load 57.5 grs of H4350 and 165 Accubonds at 2850. Some say 58.0 grs is max at that velocity. I'm sure I could go another half or even up to 58.5, but I'm where I want to be. The faster the burn rate of the powder, the quicker your pressure will rise, and you'll get higher pressures at lower velocities. Study all the data and you'll see the trends. To me the "max load listed" is the max velocity with the given powder. If I reach the max powder charge listed but am 200fps slower than the velocity listed...I'll add more powder. If I hit max velocity 1 or 2 grains short of the max powder charge, then I quit there. Velocity = pressure, but you have to factor in powder burn rate. 2850 with a 165 will give vastly different pressures with R-15, R-19 and R-22. I'd speculate you might not be able to safely reach 2850 with R-15. With R-22, you'd be at a VERY low pressure, some 9K psi short of SAAMI max according to Alliant.

These two links show the burn rate vs. velocity vs. pressure, and also show how different bullets, because of their bearing surface, can affect pressure too.

Learn to really read the data and look beyond what the "max listed powder charge" is and apply common sense, and you'll be fine. That new chrony is a valuable tool in reloading.

Reloading Data

Reloading Data

Last edited by .280Rem; 05-05-2008 at 04:30 PM.
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Old 05-06-2008, 01:40 PM
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Velocity is a great indicator of pressure
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Old 05-07-2008, 08:18 PM
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I'm not sure what to look for in velocity. When I was making up loads for my 338 win, I looked in several older printed manuals as well as some newer ones. The old books show 75 grains of IMR 4350 with a 200 grain bullet. The newer show anywhere from 71.5 to 73. I loaded up 73 and 74 grains with a 185 grain Barnes TSX. When shooting the 74 grainers I had several shots in and around the 3050-3100 mark. Then out of the blue one at 3260. No signs at all of pressures and the S.D. were very sporatic. On the 73 grains the S.D were a lot closer however just the opposite happened. Had all at or around 3120-3150 but then had one at 3000 something. Is this a sign of being overloaded, according to the Barnes manual, I'm right there on velocity. Also they printed fairly well, a completley factory gun shooting at around 3/4"-1" at 100 yards.
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Old 05-08-2008, 12:13 AM
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Quote:
Originally Posted by muleyman View Post
I'm not sure what to look for in velocity. When I was making up loads for my 338 win, I looked in several older printed manuals as well as some newer ones. The old books show 75 grains of IMR 4350 with a 200 grain bullet. The newer show anywhere from 71.5 to 73. I loaded up 73 and 74 grains with a 185 grain Barnes TSX. When shooting the 74 grainers I had several shots in and around the 3050-3100 mark. Then out of the blue one at 3260. No signs at all of pressures and the S.D. were very sporatic. On the 73 grains the S.D were a lot closer however just the opposite happened. Had all at or around 3120-3150 but then had one at 3000 something. Is this a sign of being overloaded, according to the Barnes manual, I'm right there on velocity. Also they printed fairly well, a completley factory gun shooting at around 3/4"-1" at 100 yards.
You're gonna have some that deviate. It's one reason SAAMI set things the way they did. SAAMI didn't set the MAP on the ragged edge.

Also, do you weigh each charge or just set it and throw them. Do you let your bbl cool down? A hot bbl can cause serious jumps in pressure.

Last edited by .280Rem; 05-08-2008 at 11:32 AM.
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